The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Some vehicles include an internal combustion engine that generates drive torque. More specifically, the engine draws in air and mixes the air with fuel to form a combustion mixture. The combustion mixture is compressed and ignited to drive pistons that are disposed within the cylinders. The pistons drive a crankshaft that transfers drive torque to a transmission and wheels.
A crankshaft position signal is generated based on the rotation of the crankshaft and a cylinder pressure signal is generated based on the pressure in the cylinder. A control module determines an engine position and an engine speed from the crankshaft signal and a cylinder pressure from the cylinder pressure signal. Cylinder pressure is used to control one or more subsystems within the vehicle. Errors in the cylinder pressure measurement can cause inaccurate cylinder pressure computations and therefore may cause one or more vehicle subsystems to operate inefficiently.
Cylinder pressure signals generated in the time and angle domains are used to control spark knock and combustion in the engine, respectively. A control module that determines cylinder pressure from cylinder pressure signals generated in the time and angle domains requires at least two analog-to-digital (A/D) converters, one A/D converter to sample cylinder pressure generated in the time domain and another A/D converter to sample cylinder pressure generated in the angle domain.
Cylinder pressure generated in the angle domain is typically sampled at each degree of rotation of the crankshaft. The location of each degree is predicted based on the engine position and engine speed. Variations in the engine speed may cause errors in the predicted location of each degree, which may cause errors in cylinder pressure sampled in the angle domain.